Adaptation - changes in sensitivity in response to recent stimulation - is a ubiquitous process in neural systems. It has long been theorized that adaptation should enhance perception by improving the efficiency of the neural code. While there is ample neurophysiological support for this idea, it has been difficult to find behavioral evidence of the functional consequences of adaptation, especially on brief, potentially functionally relevant timescales. I propose to use psychophysics, computational modeling, and transcranial magnetic stimulation (TMS) to investigate adaption-induced changes in the representation of brief moving stimuli. This work will bring together the behavioral and physiology literature to clarify the mechanisms of rapid adaptation and their consequences. In Aim 1 (Psychophysics and Computational Modeling), I will test the hypothesis that rapid perceptual adaptation introduces systematic errors in observers' perception of brief motion stimuli. In pilot studies, I have identified a novel perceptual phenomenon in which observers reliably perceive large, high contrast stimuli as moving in the opposite direction of the actual stimulus motion (i.e. a leftward stimulus is consistently reported as moving rightward). Using a simple computational model, I have identified a potential explanation: the model suggests that adaptation induces a spurious biphasic motion opponent signal over time. The negative lobe, signaling motion in the opposite direction, may account for observers' reversed percepts. I plan to compare these predictions with those made by alternative models. In Aim 2 (Transcranial Magnetic Stimulation), I will empirically test the models? predictions. By delivering single pulses of TMS at varying stimulus onset asynchronies (SOAs), I can recover observers' temporal integration window for brief motion stimuli. At low contrast, the model predicts that TMS will consistently impair observers' perception across SOAs. However, at high contrast, the hypothesized biphasic response predicts that early TMS (short SOA) will impair perception, but late TMS (long SOA) will improve perception. During this fellowship, I will receive training in behavioral, computational, and cognitive neuroscience methods through interactions with my research mentor, the broader NYU neuroscience community, and formal coursework. The proposed research is fully in line with the NEI mission. It investigates adaptation, an important mechanism of visual function (NEI Mission Statement). Further, as adaptation is a general property of neural systems, the proposed research in healthy observers is readily applicable to translational research in special populations, and may clarify previously observed perceptual differences in older adults as well as individuals with schizophrenia, a history of major depression, and autism.